It might replace the DS/3DS line… Nintendo have been pretty vague about that at the moment, I think they're waiting to see if the Switch sells well before they decide (kind of like the way the DS replaced the Game Boy Advance years ago). If Switch sells poorly, I think there will be a 3DS successor.
Lots of games have been announced! Granted, many of them are out on other consoles already (pretty normal for a new console), but there are still some interesting exclusives coming out this year.
Snipperclips is out at (or close to) launch, and looks really special:
Youtube Video
Zelda: Breath of the Wild is also a confirmed launch title now:
Youtube Video
Super Mario Odyssey is out later this year:
Youtube Video
A new Xenoblade has been confirmed, apparently also coming out this year:
Youtube Video
Arms, a new fighter out in a couple of months (apparently it's quite a bit deeper than the trailer shows):
Youtube Video
The latest Dynasty Warriors + Nintendo crossover, Fire Emblem Warriors:
Youtube Video
And a new Fire Emblem next year, too. Also a Splatoon sequel and an upgraded port of Mario Kart 8 this year!